1. Field of the Invention
The present invention relates to a color image forming apparatus employing the electrophotographic process and more particularly to an image forming apparatus capable of forming an electrostatic latent image.
2. Description of the Related Art
A tandem-type color image forming apparatus employing the electrophotographic process is known to include independent image forming units for respective colors to achieve high speed printing. With the tandem-type color image forming apparatus, images are sequentially transferred from respective color image forming units onto an intermediate transfer belt, and then collectively transferred from the intermediate transfer belt onto a recording medium.
Such a color image forming apparatus, when images are superimposed, produces color misregistration (positional deviation) due to mechanical factors in respective color image forming units. Particularly when a laser scanner (optical scanner apparatus) and a photosensitive drum are independently provided for each color image forming unit, a positional relation between the laser scanner and the photosensitive drum differs for each color. As a result, it becomes impossible to synchronize laser scanning positions on respective photosensitive drums, producing color misregistration.
To correct such color misregistration, the above-described color image forming apparatus applies color misregistration correction control. Japanese Patent Application Laid-Open No. 7-234612 discusses color misregistration correction control in which toner images for detecting respective colors (hereinafter referred to as toner images for detection) are transferred from photosensitive drums onto an image bearing member (intermediate transfer belt), and relative positions of the toner images for detection in the scanning and conveyance directions are detected by using optical sensors.
However, there has been the following problem in conventionally known color misregistration correction control in which toner images for detection are detected by using optical sensors. Specifically, since toner images (100%-density) for detection in color misregistration correction control are applied to the photosensitive drums and the image bearing member (belt), it takes time and effort for cleaning, resulting in reduced usability of the image forming apparatus.